Optimization of gamma-aminobutyric acid production in a model system containing soy protein and inulin by Lactobacillus brevis fermentation

Gamma-aminobutyric acid (GABA) is an active bio-compound with versatile physiological functions and, therefore, considerable attention is given to developing GABA-enriched functional foods. In this study, central composite design was used to optimize the fermentation conditions to obtain the highest GABA yield by Lactobacillus brevis. The optimal conditions of GABA production (1473.44 ppm) included 5% soy protein isolate, 3% inulin, and 96 h fermenting time at 37 °C. GABA-rich fermented solution (GABA-EFS) under optimal conditions had an appropriate emulsifying activity and water/oil holding capacity. Also, the reducing power assay revealed that GABA-EFS has electron donor groups with the ability to terminate the free radical chain reactions. Minimum inhibitory concentration results showed that Candida albicans was the most sensitive microorganism; whilst, Staphylococcus aureus and Listeria innocua were the most resistant bacteria towards GABA-EFS. In addition, GABA production was confirmed by pre-staining thin layer chromatography and fourier transform infrared spectroscopy. The results suggested that the GABA-EFS could be applied in the food industry as a functional product.